The present invention relates to a thrust reverser for a turbofan-type turbojet engine, more particularly such a thrust reverser having a thrust reversing door structure that maximizes the efficiency of the engine both in the direct thrust and the reverse thrust modes.
Fan-type turbojet engines, commonly known at as turbofan engines, have a primary duct for exhausting hot engine gases and a secondary, or cold flow, duct concentrically arranged about the primary duct. The cold flow duct communicates with a fan driven by the turbojet engine to provide additional thrust by forcing air through the cold flow duct. The fan may be mounted at the front or near the rear portion of the turbojet engine.
In such turbofan engines having a relatively high bypass ratio, (i.e., the ratio between gases passing through the secondary duct and those gases passing through the primary duct) it is known to have a thrust reversing device acting on only the air passing through the cold flow duct.
A typical thrust reverser applied to the cold flow duct of a turbofan engine is illustrated in FIG. 1. The upstream portion of the housing which defines the outer limits of the cold flow duct and which is concentrically arranged about the primary duct (not shown) is designated as 1 and generally comprises an external housing panel 4, an internal housing panel 5 with frame 6 interconnecting the external and internal panels. The outer surface of external panel 4 defines an airflow surface over which air external to the engine, indicated by arrow 10, passes during flight of the aircraft. The inner surface of internal panel 5 defines the outer boundary of the cold flow duct through which air, indicated by arrow 15, passes.
A thrust reverser is illustrated generally at 2 and an downstream fairing of the housing is illustrated at 3. The thrust reverser 2, in known fashion, comprises a door 7 pivotally attached to the housing such that it is movable between a closed position, illustrated in FIG. 1, during the forward thrust operational mode of the engine, and an open position in which the upstream end of the thrust reverser door is moved radially outwardly into the external airstream, while the downstream portion is moved radially inwardly into the cold flow duct airstream so as to redirect the cold flow duct air laterally through an opening in the housing in a direction which has a reversing thrust component.
The actuator 7a for moving door 7 between its opened and closed positions may comprise an hydraulic cylinder extending through and mounted to frame member 6 and having an extendable and retractable piston rod connected to the thrust reverser door 7.
The thrust reverser door 7 has an outer door panel 9, and an internal door panel 11 joined together by internal structure 12. The upstream end of the door 7 has a deflector 13 to maximize the efficiency of the thrust reverser when the door 7 is in the opened, or thrust reversing position. When the door is in the closed, or forward thrust position as illustrated in FIG. 1, the outer door panel 9 has an external surface which substantially flush with those of upstream external panel 4 and downstream fairing cone 3. Although only one thrust reversing door 7 is illustrated in FIG. 1, it should be understood that more than one door may be utilized, depending upon the operational characteristics of the aircraft engine and the aircraft with which the thrust reversing structure is associated.
In order to maximize the efficiency of the thrust reversing door when in the open position, the deflector 13 must extend beyond the inner surface of internal door panel 11. Thus, the radial distance between upstream portions of the outer door panel 9 and the internal door panel 11 is somewhat less than the radial distance between downstream portions of these panels. While this maximizes the efficiency the thrust reversing position, it creates problems when the door 7 is in the closed position. By locating the external door panel 9 substantially flush with the upstream and downstream external surfaces, external air flow, indicated by arrow 10 passes over the outer surface of the housing with minimal disruptions or perturbations. However, the orientation of the internal door panel 11 creates a cavity 16 defined by the internal door panel 11, the deflector 13, the deflecting edge 8 and the theoretical line 14 interconnecting the internal surfaces of the housing and the downstream rear fairing cone. Line 14 indicates an ideal surface that would minimize the disruptions and perturbations in the air flow 15 flowing through the cold flow duct. A portion of the air in the cold flow duct follows the deflecting edge 8 and enters cavity 16, thereby creating aerodynamic deficiencies in air flow through the cold flow duct which are detrimental to the operation of the device in the forward thrust mode. Such typical examples of thrust reversers can be found in U.S. Pat. No. 4,485,970 to Fournier et al as well as in French patent Nos. 2,486,153; 2,559,838; and 2,030,034.
U.S. Pat. No. 3,605,411 to Maison et al describes a thrust reverser having pivoting doors for deflecting the cold flow air passing through the cold flow air duct through a lateral opening in the housing. In this device, the outer door panel and the internal door panel are separately pivotally attached to the stationary housing such that each pivots about a different axis. This enables a differential pivoting movement between the respective panels to expose a portion of the upstream deflector when the door is in the thrust reversing mode and to align the internal door panel with the internal surfaces of the housing at upstream and downstream locations from the door when in the forward thrust mode. While the device has somewhat alleviated the problems associated with the other prior art devices, the separate mountings of the door panel and the mechanism for actuating the panels has proven to be rather complex, thereby decreasing the reliability and safety of the system.